Calculator
Plumbing Gas Pipe Sizing Calculator
Add up the appliances on a gas run, measure the developed length to the most remote outlet, and get the minimum Schedule 40 pipe size from the NFPA 54 / IFGC capacity table — with connected load in BTU/hr and CFH, the length column used, spare capacity, and every other size at that length. Free, no signup.
Free
Appliances on this run
Use the nameplate input rating where you have it — the defaults are IFGC Table 402.2 typical values. Every appliance the run feeds counts, whether or not it fires at the same time.
| Appliance | BTU/hr | Qty | Remove |
|---|---|---|---|
Advanced
Natural gas60 ft column
Minimum pipe size
1"
240,000 BTU/hr connected · 240 CFH
At the table limit7% spare capacity
IFGC Table 402.4(2) / NFPA 54 Table 6.2.1(B) — Schedule 40 metallic pipe, natural gas, 0.5 in. w.c. drop, 60 ft column
- Less than 10% spare capacity — any added fitting length or a future appliance pushes this run over. Consider the next size up.
This run at a glance
Total connected load
240,000 BTU/hr240 CFH at 1,000 BTU/ft³
Table length used
60 ftExact column in the code table
Capacity at that size
257 CFH257,000 BTU/hr
Spare capacity
7%17 CFH of headroom for future appliances
Capacity by pipe size
Every Schedule 40 size at the developed length you entered, so you can see what the next size up buys you.
| Size | Capacity | BTU/hr |
|---|---|---|
| 1/2" | 65 CFH | 65,000 |
| 3/4" | 137 CFH | 137,000 |
| 1"minimum | 257 CFH | 257,000 |
| 1-1/4" | 528 CFH | 528,000 |
| 1-1/2" | 791 CFH | 791,000 |
| 2" | 1,520 CFH | 1,520,000 |
| 2-1/2" | 2,430 CFH | 2,430,000 |
| 3" | 4,290 CFH | 4,290,000 |
| 4" | 8,760 CFH | 8,760,000 |
Load breakdown
| Appliance | Qty | BTU/hr | CFH |
|---|---|---|---|
| Furnace — 100,000 BTU | 1 | 100,000 | 100.0 |
| Range — freestanding | 1 | 65,000 | 65.0 |
| Water heater — 40 gal tank | 1 | 40,000 | 40.0 |
| Clothes dryer | 1 | 35,000 | 35.0 |
Industry benchmarks
Standard pressure drop
0.5 in. w.c.IFGC Table 402.4(2) / NFPA 54 Table 6.2.1(B) for a 7 in. w.c. natural-gas system.
Natural gas heating value
1,000–1,030 BTU/ft³Divide appliance BTU/hr by this to get the CFH the table is indexed on.
Propane heating value
2,516 BTU/ft³Also 91,502 BTU per gallon of liquid propane.
Gravity multiplier at 1.50 sg
× 0.63IFGC Table A102.4 — converts the 0.60-sg table capacity to undiluted propane.
What you'll get
List the appliances on the run
Pick from typical furnace, water heater, range, dryer, fireplace, grill, pool heater and generator loads — or type the nameplate BTU/hr input. Defaults follow IFGC Table 402.2 where the code lists a value. You can also enter one total connected load instead.
Enter the longest developed length
Measure from the meter or second-stage regulator to the most remote outlet, including equivalent length for fittings. That single length sizes every section of the run — the longest-length method in IFGC 402.4.1.
Read the minimum pipe size
Get the smallest Schedule 40 size that carries the load at that length, the table capacity in CFH and BTU/hr, spare capacity percent, the exact code citation, and a per-size table so you can see what the next size up buys you.
How it works
- 1
List the appliances on the run
Pick from typical furnace, water heater, range, dryer, fireplace, grill, pool heater and generator loads — or type the nameplate BTU/hr input. Defaults follow IFGC Table 402.2 where the code lists a value. You can also enter one total connected load instead.
- 2
Enter the longest developed length
Measure from the meter or second-stage regulator to the most remote outlet, including equivalent length for fittings. That single length sizes every section of the run — the longest-length method in IFGC 402.4.1.
- 3
Read the minimum pipe size
Get the smallest Schedule 40 size that carries the load at that length, the table capacity in CFH and BTU/hr, spare capacity percent, the exact code citation, and a per-size table so you can see what the next size up buys you.
How the longest-length method actually sizes a gas line
Gas pipe sizing trips people up because it is not a per-section calculation. The longest-length method measures one distance — from the point of delivery to the most remote outlet — finds that length in the capacity table, and then sizes every section of the system off that single row. A branch ten feet from the meter still gets read from the 100-foot row if the most remote outlet is 100 feet away. The code is explicit that where the measured length falls between two columns you use the next longer distance, and where the demand falls between two figures you take the next larger one, so the answer is always the conservative side of the table.
The tables themselves are indexed on volume, not heat: capacity is published in cubic feet per hour at 0.60 specific gravity for a half-inch water column pressure drop, so appliance BTU/hr ratings have to be divided by the local heating value first — roughly 1,000 to 1,030 BTU per cubic foot for natural gas, 2,516 for undiluted propane. Propane also carries a specific gravity of 1.50 rather than 0.60, so the code applies a 0.63 multiplier to the table capacity. This calculator does all three steps and shows its work, including which length column it landed on and how much headroom the chosen size leaves.
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View statesGas Pipe Sizing Calculator FAQs
How do I convert appliance BTU/hr to CFH for gas pipe sizing?
Divide the total connected BTU/hr input by the heating value of the gas. Natural gas is typically 1,000 to 1,030 BTU per cubic foot, so 240,000 BTU/hr is about 240 CFH. Undiluted propane is 2,516 BTU per cubic foot (91,502 BTU per liquid gallon), so 250,000 BTU/hr is about 99 CFH. Your utility can give you the exact local heating value, and the calculator lets you override the default.
What is the longest-length method?
It is the standard sizing method in IFGC 402.4.1. You measure the developed length from the point of delivery to the most remote outlet, locate that length in the capacity table (or the next longer column if it falls between two), and then size every section of the system from that one row using each section’s own connected load. It is deliberately conservative — the branch-length method sizes each branch from its own measured length instead and generally gives smaller pipe.
Does this work for CSST or copper gas line?
No, and the calculator will say so rather than give you a number. The Schedule 40 table applies to black iron and steel pipe only. CSST is sized from the manufacturer’s listed EHD tables (Gastite, TracPipe, Wardflex) and those ratings are not interchangeable with nominal Schedule 40 sizes. Semi-rigid copper has its own tables, IFGC 402.4(5) and 402.4(6), and is not permitted for fuel gas in every jurisdiction.
Can I install gas pipe from this calculator alone?
No. This is a screening tool for field estimates, takeoffs and customer conversations. The authority having jurisdiction and the full code table govern the final design — including fitting equivalent lengths, elevation and regulator effects, two-stage and elevated-pressure systems, appliance connector sizing, and any local amendments. Gas work must be sized, installed, pressure-tested and inspected by a licensed contractor under the adopted fuel gas code.
